1. Field of the Invention
The present invention relates to an intake apparatus for an engine and, more particularly, to an intake apparatus for an engine having a surge tank with an intake-air increasing chamber on an intake passage.
2. Description of the Prior Art
Many engines, particularly engines for automobiles, have a surge tank with an intake-air increasing chamber on an intake passage. As the surge tank has a considerably large volume, it is usually mounted over the engine.
Recently, multiple cylinder engines have been developed with the attempt to improve a charging efficiency by the supercharging due to dynamic effects such as an inertial effect. They are designed such that a surge tank is connected to a plurality of cylinders disposed in an engine body separately with a separate intake tube. For those engines, it is desired to make each of the separate intake tubes as long as possible in order to achieve dynamic effects in the range of a low engine speed. The longer the length of the separate intake tube is, the lower an engine speed producing the dynamic effects is. It is a matter of course that the lengths and the sizes of the separate intake tubes are rendered equal to each other in order to allow each cylinder to achieve the dynamic effects of the intake air in an equal manner.
As have been described above, in instances where a long separate intake tube is used, it is important how to arrange for such long separate intake tubes in an engine room in order to compact an engine as a whole. In particular, for an engine body having a plurality of cylinders, it is the issue how to minimize a degree of protrusion of the separate intake tubes toward one side surface of an engine body because the engine body is provided on one side surface thereof with a plurality of intake ports extending from the cylinders.
Japanese Utility Model Application (Early Publication) No. 175,666/1984 discloses an arrangement for a surge tank so as to extend in the direction of the cylinder arrangement and be mounted over an engine body, while separate intake tubes connecting independently plural intake ports to the surge tank are each of a curved shape. More specifically, the separate intake tube is designed so as to extend in a direction apart from one side surface of the surge tank and then be curved in a U-shaped manner turning toward one side surface, i.e., an intake port, of the engine body. With this arrangement, a degree of protrusion of each of the separate intake tubes from the one side surface of the engine body can be rendered equal to each other, while the degree can be minimized as small as possible.
However, such an arrangement for the separate intake tubes does not satisfy a demand for a reduction in the degree of protrusion of the separate intake tubes from one side surface of the engine body. In particular, an engine for an automobile is provided around the engine body with a variety of large-size instruments and devices, and it is anticipated in some cases that a curved portion of each of separate intake tubes located on one end side in the direction of the cylinder arrangement may block an arrangement of such instruments and devices. For example, in an automobile, there is used a servo apparatus for increasing an force pressed on a brake pedal in many cases. The servo apparatus is generally of the type using a pressure differential between the intake negative pressure and the atmospheric pressure. The servo apparatus of this type has usually a large diameter. Accordingly, in instances where an engine body is accommodated in an engine room formed in the front of a vehicle chamber in such a manner that, for example, cylinders are arranged in a lengthwise direction of the vehicle body, the problem will arise that the installment or detachment of the servo apparatus is caused to be very inconvenient because it is impossible to ensure a sufficient space in the transverse direction between curved portions of separate intake tubes positioned at one end side in the direction of the cylinder arrangement on the rear side of the vehicle body and the servo apparatus.
Furthermore, recently, many attempts have been made such that a control valve is mounted in each of the separate intake tubes, as have been described hereinabove, so that a degree of an opening of the control valve is designed so as to be controlled in accordance with a mode of operation of an engine. The plural control valves are driven by one actuator so that a connecting shaft is rotatively held with the separate intake tubes and the actuator is coupled with the control valves through the connecting shaft. In this case, in order to avoid as much as possible that the actuator protrudes to a large extent toward the end side in the direction of the cylinder arrangement of the engine, the actuator is mounted nearly at the middle position among the plural separate intake tubes in the direction of the cylinder arrangement and the connecting shaft is divided into two nearly at the middle portion in the direction of the cylinder arrangement, as disclosed in Japanese Patent Application (Early Publication) No. 192,825/1984. However, as the connecting shaft is divided into two, it is necessary to cause at least one portion to be exposed to the outside for each of the divided connecting shaft portion. In other words, at least two portions are required to be exposed to the outside for one connecting shaft. This results in the fact at least two portions are required to seal the inside of the separate intake tube from the outside. This is the disadvantage in terms of preventing a seal leakage.